1. Field of the Invention
The present invention relates to a system and method for controlling fuel injection of a common rail fuel system in a multi-cylinder internal combustion engine.
2. Background Art
Common rail fuel systems are used in various types of internal combustion engines, such as diesel engines, for example. An accumulator or rail is used to distribute fuel to injectors or nozzles associated with each cylinder of the engine. An engine control module communicates with various engine components including one or more fuel pumps and fuel injectors to meter the fuel delivered to each cylinder, i.e. control the quantity and timing of the fuel delivery to ultimately control the performance and emissions of the engine.
A number of strategies have been developed to control fuel injection in an attempt to improve engine performance and fuel economy while reducing emissions. One such strategy employs multiple fuel injections during a single combustion cycle. Depending upon the particular application and operating conditions, the fuel injection for a single combustion cycle may be split into a pilot injection, a main injection, and one or more post injections, for example. The quantity and timing of each injection should be accurately controlled to achieve the intended benefits of using multiple injections, particularly for the pilot and post injections because of their relatively smaller volumes and short durations. However, many factors affect the injection events, such as common rail fuel pressure and injector energizing time, for example, making this a difficult task to accomplish. One prior art control strategy used for conventional fuel systems employing electronic unit injectors (EUIs) determines the beginning of injection for the main injection based on the-beginning of injection time and the duration of the pilot injection. While this strategy is acceptable for conventional EUI systems, for a common rail system the durations of the pilot and post injections are a function of the fuel pressure within the common rail and are therefore difficult to accurately control.
The present inventors have recognized various shortcomings of the prior art approaches and have developed a system and method for controlling multiple fuel injections for common rail fuel systems that is believed to provide more accurate control, particularly during transient operating conditions, which may contribute to improved engine performance and fuel economy while reducing emissions.
The present invention provides a system and method for controlling multiple fuel injections during a single combustion cycle for a multiple cylinder internal combustion engine having a common rail fuel distribution system with the beginning of injection for the pilot and main injections based on crankshaft position while post injections are based on the main injection timing and an injector turn on delay and/or turn off delay determined using actual rail pressure. A rail pressure setpoint is determined based on current engine operating conditions including one or more fluid temperatures and current operating mode to provide more accurate injection control.
The present invention also includes computer readable storage media having stored instructions executable by a computer to control multiple fuel injections during a single combustion cycle for a multiple cylinder internal combustion engine having a common rail fuel distribution system with the beginning of injection for the pilot and main injections based on crankshaft position while post injections are based on the main injection timing and an injector turn on delay and/or turn off delay determined using actual rail pressure. The computer readable storage media may also include instructions for determining a rail pressure setpoint based on current engine operating conditions including engine operating mode and one or more fluid temperatures.
The present invention provides a number of advantages. For example, the present invention controls the injection timing for pilot and main injections based on crankshaft position rather than allowing the main timing to be a function of actual rail pressure through pilot injection timing, energizing time, and pilot-to-main injection gap. This provides better control of the relatively smaller quantity and shorter duration pilot injection and more consistent main injections. In addition, the present invention provides a strategy that is generally easier to calibrate and provides more precise control of the actual beginning of injection, particularly for the main injection when multiple injection mode is active.